goffered again - I think Occasional Aviator was meaning that the Mk3 can turn on the spot, so to speak, even with twin mains. 'castor' is the switch position to get the nosewheel to turn to the 90 deg position to allow a spot turn, normally the steering is restricted to 45 deg either way. It seemed to confuse the poor marshaller the first time we took one for a visit (can't remember if it was Benson or Odiham or wherever), he wasn't used to stuff that could turn on the spot. The spot around which it turns is where the Deck-lock is on the RN aircraft, so you can spin around with the deck-lock engaged. As always my memory is about 4 years out of date.
I can't see why the RN ones couldn't have twin wheels, I seem to remember the oleos and sponson where the same anyway, and I can't sea how deck handling would have been made more difficult.
If I was bobbing around some nice cold bit of sea, anything would look good to me, even a RAN Seapsrite, which looks pretty ugly in any other situation.